diff --git a/apps/kolab_guam/src/kolab_guam_session.erl b/apps/kolab_guam/src/kolab_guam_session.erl
--- a/apps/kolab_guam/src/kolab_guam_session.erl
+++ b/apps/kolab_guam/src/kolab_guam_session.erl
@@ -238,17 +238,14 @@
 preprocess_client_data(undefined, Data, #state{ buffered_client_data = Buffered }) ->
     <<Buffered/binary, Data/binary>>;
 preprocess_client_data(Z, Data, #state{ buffered_client_data = Buffered }) ->
-    Inflated = joined(zlib:inflate(Z, Data), <<>>),
+    Inflated = iolist_to_binary(zlib:inflate(Z, Data)),
     <<Buffered/binary, Inflated/binary>>.
 
 postprocess_server_data(undefined, Data) ->
     %% we aren't compressing so there is nothing to do
     Data;
 postprocess_server_data(Z, Data) ->
-    joined(zlib:deflate(Z, Data, sync), <<>>).
-
-joined([], Binary) -> Binary;
-joined([H|Rest], Binary) -> joined(Rest, <<Binary/binary, H/binary>>).
+    iolist_to_binary(zlib:deflate(Z, Data, sync)).
 
 init_rules(RuleConfig) -> init_rule(RuleConfig, []).
 init_rule([], Acc) -> Acc;